Generally, for the spray coating of an object having a comparatively large coating surface, like body of an automobile, furniture or electric appliances, a coating method is well known whereby the coating surface of the object to perform coating is divided into a plural number of segments (see, for example, Japanese Patent Laid-Open No. 2003-144990).
According to the arrangement disclosed in this prior art, two sprayer units are arranged on either right side and left side of the body of an automobile, and the upper surface of the body is coated by being divided into left and right coating areas. In this case, relative to the hood (bonnet) and the roof of the body of an automobile, the two sprayer units reciprocate (to the front and to the rear) in conveying directions of the body of an automobile and coat the individual coating areas.
To coat a large automobile, for example, coating surface will be larger than the amplitude (stroke) of the reciprocation of a sprayer unit in the conveying direction. Thus, when coating is performed, the coating surface must be divided into a plural number of coating areas in the conveying direction. In this case, when the conveying speed of the automobile body is slow and the size of the area coated per unit hour is comparatively small, a plural number of coating areas can be coated by use of a single sprayer unit. However, when the conveying speed of the automobile body is high, the size of the area to be coated per unit hour is increased and all the coating areas can not be coated by use of a single sprayer unit. Therefore, either the number of sprayer units must be increased to reduce the coating rate imposed on each sprayer unit or a tracking device must be employed to synchronize the movements of the sprayer unit to the automobile body and the coating available range must be expanded.
However, the increase in the number of sprayer units or the addition of equipment for a tracking device increases the initial costs associated with the introduction of the machines or the installation of other devices. In addition, since the size of the coating booth would be increased, other problems are that the cost of equipment for the coating booth and the cost of providing air conditioning are increased.